There is an immense interest in hybrid nanocomposite materials with periodic structures, since they have potential applications in production of photonic or photonic crystals, in optical data storage, in chemical and biochemical sensing, and in optical limiting and switching. Microbeads doped with NPs were used for biological labelling. (Han, M.; Gao, X.; Su, J. Z.; Nie, S. Nature Biotechnol. 2001, 19, 631). Photonic crystals produced from microspheres doped with semiconductor NPs showed coupling of structurally- and angularly-dependent electromagnetic resonances (arising from microscale structural periodicity) and optical properties of the semiconductor quantum dots (providing spectral control through the quantum confinement effect) ((a) Blanco, A.; López, C.; Mayoral, R.; Míguez, H.; Meseguer, F.; Mifsud, A.; Herrero, J. Appl. Phys. Lett. 1998, 73. 1781-1783; (b) Vlasov, Yu. A.; Luterova, K.; Pelant, I.; Hönerlage, B.; Astratov, V. N. Appl. Phys. Lett. 1997, 71, 1616-1618; (c) Lin, Y, Zhang, J.; Sargent, E. H.; Kumacheva, E. Appl. Phys. Lett. 2002, 81, 3134)). Control over assembly of microspheres doped with magnetic NPs in periodic structures was achieved under the action of magnetic field ((a) Xu, X. L.; Majetich, S. A.; Asher, S. A. J. Am. Chem. Soc. 2002, 124, 13864; (b) Lyubchanskii, I. L.; Dadoenkova, N. N.; Lyubchanskii, M. I.; Shapovalov, E. A.; Rasing, T. H. J. Phys. D. 2003, 36, R277). Alternatively to solid microspheres, colloid crystals produced from microgels or metal NPs-doped microgels were used for the patterning of self-assembled photonic materials. ((a) Hellweg, T.; Dewhurst, C. D.; Bruckner, E.; Kratz, K.; Eimer, W. Colloid Polym. Sci. 2000, 278, 972; (b) Hu, Z.; Lu, X.; Gao, J. Adv. Mater. 2001, 13, 1708; (c) Debord, J. D.; Eustis, S.; Debord, S. B.; Lofye, M. T.; Lyon, L. A. Adv. Mater. 2002, 14, 658662; (d) Lee, Y.-J.; Braun, P. V.; Adv. Mater. 2003, 15, 563-566; (e) Jones, C. D.; Lyon, L. A. J. Am. Chem. Soc. 2003, 125, 460)).
A “bottom-top” approach to producing materials with structural hierarchy is particularly attractive to chemists as it is a versatile and simple method to producing such materials. In this strategy, small structural units (building blocks) with useful functionalities are assembled in periodic arrays to produce materials with periodically modulated composition, structure and function.
Recently, the inventor developed a “core-shell” strategy for synthesis and fabrication of periodically structured polymer-based materials. (Kumacheva, E.; Kalinina, O.; Lilge, L. Adv. Mater. 1999, 11, 231; Kalinina, O., Kumacheva, E. Macromolecules 1999, 32, 4122; Kalinina, O.; Kumacheva, E. Chem. Mater. 2001, 13, 35; Kalinina, O.; Kumacheva, E. Macromolecules 2002, 35, 3675). The overview of the “core-shell” approach is given in FIG. 1. Polymer or polymer-based core-shell particles with dimensions varying from 100 nm to several microns are synthesized in Stage A. The essential feature of these particles is a specific relation between the glass transition temperatures, Tg, of the core-forming polymer (CFP) and the shell-forming polymer (SFP): the glass transition temperature of the SFP is substantially lower than that of the CFP, that is, Tg,SFP<Tg,CFP. Following synthesis, the core-shell microspheres are assembled in a periodic one-, two-, or three-dimensional array (Stage B) and annealed at the temperature Tg,SFP<Tannealing<Tg,CFP (Stage C). During heat processing the SFP softens, flows, and ultimately forms a continuous matrix, while the GFP remains intact. The morphology of the resulting material is shown in stage C of FIG. 1.
The core-shell particles can be obtained using (a) synthesis of particle cores accompanied by the synthesis of latex shells on the surface of cores, (b) electrostatically-driven heterocoagulation between the oppositely charged large particles of the CFP and small particles of the SFP followed by spreading of the SFP over the surface of the core during heat processing or by (c) controlled phase separation technique (Okubo, M.; Lu, Y., Colloids Surf. A 1996, 109, 49; Ottewell, R. H., Schofield, A. B.; Waters, J. A.; Williams, N. S. Colloid Polym. Sci. 1997, 275, 274; Furusawa, K., Velev, O. D. Colloids Surf. A 1999, 159, 359; Han, J.; Kumacheva, E. Langmuir 2001, 17, 7912; Li., H.; Kumacheva, E. Colloid Polym. Sci. 2003, 281, 1; Dudnik, V.; Sukhorulkov, G. B.; Radtchenko, I. L.; Mohwald, H. Macromolecules 2001, 34, 2329).
The core-shell strategy provides several degrees of freedom over morphology and composition of the ultimate material. The “compositional” degrees of freedom can be divided into two groups. First, the core and the shells can be synthesized from the materials with distinct compositions and properties, such as organic or inorganic polymers or conductive and dielectric organic polymers. Alternatively, the encapsulation of inorganic cores with polymeric shells produces core-shell functional building blocks for periodic mesostructured hybrid materials.
In the second strategy, the core-shell particles are synthesized from the similar polymers (still keeping the required relation between their glass transition temperatures), however, in the stage of synthesis or after synthesis, the core and/or the shell are chemically functionalized or physically doped with different low-molecular weight species. As a result of confinement in the microbeads, these species form spatially localized mesoscopic domains in the ultimate composite material. Fluorescent dyes, chromophores, molecules with properties useful in nonlinear optics, and organic and inorganic nanoparticles can be selectively incorporated in the core-shell polymer beads thus tailoring novel optical, magnetic or electric properties to the ultimate material. This approach is shown in FIG. 2 where the nanoparticles are incorporated in the core or the shell of the polymer beads. Alternatively, different nanoparticles can be localized in the cores and shells. Each of these combinations would lead to a particular compositional pattern in the composite material, shown in FIG. 2.
In recent years, the modification of polymer microspheres with inorganic semiconductor nanoparticles (NPs) has stimulated great interest in materials science due to the possibility of combining polymer processability and intrinsic properties of NPs, such as their catalytic, magnetic and electronic properties. Polymer microbeads were synthesized in the presence of pre-formed NPs (Kronick, P. L.; Campbell, G. L.; Joseph, K. Science 1978, 200, 1074; Frank, S.; Lauterbur, P. C. Science 1993, 363, 334; Sauzedde, F.; Elaisari, A.; Pichot, C. Colloid Polym. Sci. 1999, 277, 1041; Horak, D. J. Polym. Sci. Part A Polym. Chem. 2001, 39, 3707; Xu, X.; Friedman, G.; Humfeld, K. D.; Majetich, S. A.; Asher, S. A. Chem. Mater. 2002, 14, 1249) or they were mixed with preformed NPs, the latter either adsorbed to the surface of microspheres, or diffused inside the polymer particles. (Haloui, L. I. Langmuir 2001, 17, 7130).
Alternatively, NPs were synthesized in-situ, that is, inside polymer spheres, e.g., in ion-exchange resin beads or in microgel particles. (Winnik, F M.; Momeau, A.; Ziolo, R. F.; Stoever, H. D.; H.; Li, W.-H. Langmuir 1995, 11, 3660; (b) Antonietti, M.; Grohn, F.; Hartmann, J.; Bronstein, L. Angew. Chem. Int. Engl. Ed. 1997, 36, 2080).
Among these methods, the in-situ synthesis provides a higher doping level, precise control over NP size and a more homogenous distribution of the NPs in the polymer microsphere.
It would be desirable to provide a method of producing composite colloidal polymer/inorganic nanoparticle materials economically and which is versatile allowing one to tune the properties of the nanoparticles by changing the composition of the colloidal polymer. These colloidal polymer/inorganic nanoparticle materials could then act as the functional building blocks in fabrication of hybrid nanocomposite materials.